The present invention relates to a device using a sensor for a small rotation angle. More particularly, the invention relates to a device using a sensor capable of detecting a small rotation angle of an object that has a small area for reflecting light.
Since atomic force microscopy was first proposed by G. Binning inPhys. Rev. Letters Vol. 58, No. 9, pp. 930 (1986), a number of improvements have been made on the technology and new applications thereof have been undertaken. Illustratively, European Patent Laid-Open No. 290648 (Nov. 17, 1988) proposes a method for eliminating disadvantages involved in detecting the displacement of a cantilever by use of a tunneling current, the proposed method detecting the cantilever displacement in terms of capacitance or optical interference. In Appl. Phys. Lett. 53(12), Sep. 19, 1988, pp. 1045-1047, G. Meyer et al propose a laser beam deflection detection method under the title of "Novel optical approach to atomic force microscopy." This method is intended to remove deficiencies stemming from detecting the cantilever displacement by optical interference.
To such advances in atomic force microscopy, the inventors of the present invention have also contributed some improvements that go beyond the traditional scope of atomic force microscope. Specifically, they have proposed, among others, such applications as "Surface observing apparatus" in U.S. Pat. No. 5,436,448, "Scanning probe microscope and method of control error correction" in U.S. Pat. No. 5,467,642, "Precision machining method, precision machining apparatus and data storage apparatus using the same" in U.S. Pat. No. 5,471,064, and "A device for recording information in a size of several tens of nanometers or less by applying the principle of an atomic force microscope" in U.S. patent application Ser. No. 09/142,663.
In the devices proposed above, the displacement of a free end of the cantilever is detected as a small rotation angle through the use of the laser beam deflection detection method proposed by G. Meyer et al. Today, this method is one of the most commonly utilized techniques for detecting a small rotation angle of the cantilever.
The laser beam deflection detection method works primarily as follows: light from a light source is first reflected on a surface of a measuring object. When the measuring object (i.e., its reflecting surface) is rotated by an angle of .theta., reflected light is changed in orientation by an angle of 2 .theta. in the same direction as that of the rotation of the measuring object according to the principle of reflection. If the angle .theta. is sufficiently small, a beam of reflected light is displaced from its initial position by 2L .theta. at a distance of L from the reflecting surface. If the distance L is sufficiently long, the displacement of the light beam may be made large enough to allow the rotation angle of the measuring object to be sensed by a detector for detecting light spot displacement.